CUBN and megaloblastic anemia: IGS is caused by mutations in cubilin (CUBN) or amnionless (AMN) gene, which encode for the subunits of the heteromeric receptor known as cubam, highly expressed both in epithelial brush borders of the distal small intestine (which mediates the uptake of cobalamin) and renal proximal tubules (for the reuptake of albumin) [2].